Floating roof drain

ABSTRACT

A self-actuating drain for a floating roof storage tank, adapted to drain excess liquid from above a sunken floating roof to below the floating roof. The siphon drain comprises a generally inverted U-shaped pipe having first and second upstanding leg portions connected together at the respective upper ends by a connecting portion with the bottom end of the second leg portion extending below the floating roof and the bottom end of the first leg portion being positioned above the floating roof. A check valve means is attached to the connecting portion between the two leg portions to allow air to escape from the inverted U-shaped pipe.

' Appl. No.: 137,007

Related US. Application Data Division of Ser. No. 15,112, Feb. 27, 1970.

References Cited UNITED STATES PATENTS 8/1958 Larsen 220/26 D 11/1911Meyer 4/48 United States Patent 1 1 [111 3,756,265 Wagoner et al. Sept.4, 1973 [54] FLOATING ROOF DRAIN 298,805 5/1884 Weeden 137 128 354,45612/1886 Atkinson et al.. 137 137 [75] InventorsRoberm'wagonerGnffithvKL? 517,093 3/1894 Cattanach 137/137 J Kmghol'll,HOUSIOWTBX- 963,231 7/1910 Mahoney 137/128 [73 Assignee: 7 AerojetGeneral Corporation,

5 Elmont C lif Primary Exammer-Jlenry T. Klmkslek 1. Attorney-E. O.Ansell [22] Filed: Apr. 23, 1971 [5 7 ABSTRACT A self-actuating drainfor a floating roof storage tank, adapted to drain excess liquid fromabove a sunken floating roof to below the floating roof. The siphondrain comprises a generally inverted U-shaped pipe having first andsecond upstanding leg portions connected together at the respectiveupper ends by a connecting portion with the bottom end of the second legportion extending below the floating roof and the bottom end of thefirst leg portion being positioned above the floating roof. A checkvalve means is attached to the connecting portion between the two legportions to allow air to escape from the inverted U-shaped pipe.

2 Claims, 3 Drawing Figures FLOATING ROOF DRAIN This application is adivision of our co-pending application Ser. No. 15,112, filed Feb. 27,1970 now US. Pat. No. 3,606,071, issued Sept. 20, 1971.

BACKGROUND OF THE INVENTION This invention relates to liquid storagetanks of the type provided with a movable roof or deck which floats uponand is supported by the liquid in the tank. It particularly relates to amethod and apparatus which will efficiently and automatically removeliquid from a sunken pan type floating roof without the assistance ofpersonnel entering the tank and without structural damage to the roof.

The roofs in floating roof installations may sink because, for example:

1. Out-of-roundness of the tank shell due to settlement of thefoundation. The pan binds on the shell and tilts as the liquid levelchanges causing liquid to overflow into the pan.

2. lmproper operation of mixers may throw liquid into the pan. I

3. A rapid insertion of gas-laden liquid under the deck may createtilting due to a gas bubble which binds the pan to the tank shellcausing liquid to over-flow the pan.

4. Rain water may accumulate in the pan.

In short, the roof will sink whenever the weight of the roof plus liquidaccumulated in the pan is greater than the weight of a volume of liquidequal to the volume displaced by the roof. I

The floating roof frequently has support legs to sup port the roof onthe floor of the tank. These legs, especially in covered floating rooftanks, are not designed to support any load except the weight of the panand a few'inches of liquid standing above the pan. Since the rim of thepan is about inches high, it is possible for a 15 inch liquid level toform on the pan when the pan is on its legs on the floor of the tank.This amount of liquid will do no harm as long as it is balanced by acounter pressure of liquid underneath the pan. But, when liquid iswithdrawn from the tank to allow workers to repair the tank and thesunken roof, then the liquid underneath the pan must be removed, thusresulting in an unbalanced force of 15 inches of liquid above the panwhich cannot normally escape. The economically designed legs can notsupport the roof and such liquid and will fail.

in the past two methods have been used to unload product from the pan ofa sunken roof. First, a hot tap may be made into the tank shell througha welded fitting and the product then removed by a suction appara tus.Second, a workman may walk onto the sunken roof with an oxygen mask tomanually remove the drain plug, which is located in the center of theroof for this type of emergency use. Both of these methods arehazardous, costly and require experienced personnel. Thus, a simple,safe, economical method and apparatus for removing the liquid productfrom above the roof is required.

SUMMARY OF THE INVENTION Therefore, one object of this invention is toprovide a method of removing liquid from a sunken pan type floating roofthat is simple, safe, and economical.

Another object is to provide a methodof removing liquid from a sunkenpan type floating roof without causing structural damage to the floatingroof.

A further object is to provide an apparatus which will efficiently andautomatically remove liquid from a sunken pan type floating roof withoutthe assistance of personnel entering the tank and without structuraldamage to the floating roof.

To attain these and other objectives the present invention provides anovel method and apparatus to remove the accumulated liquid from theroof pan automatically at the same time the liquid is being removed frombelow the pan. The invention utilizes the theory of an ordinary siphon.A siphon is a pipe or tube bent to form two legs of unequal length, bywhich a liquid can be transfered to a lower level, over an intermediateelevation, by atmospheric pressure forcing the liquid up the shorterbranch of the pipe immersed in it, while the excess of weight of theliquid in the longer branch (when once filled) causes a flow. Trappedair or other gas present within the pipe will prevent flow of liquidunless there is provision for removing the air.

The present method comprises the steps of: withdrawing liquid from belowthe sunken floating roof; and siphoning liquid from above the floatingroof to below the floating roof when the liquid level in the tank isbelow the accumulated liquid above the floating roof. The rate of liquidflow from below the floating roof should be equal to or less than therate of liquid flow being siphoned from above the floating roof to belowDESCRIPTION OF THE DRAWING The invention, both as to its organizationand method of operation, taken with further objects and advantagesthereof, will best be understood by reference to the followingdescription taken in conjunction with the accompanying drawing, inwhich:

FIG. 1 is a cross-sectional view of a storage tank embodying thefeatures of the present invention, illustrating the floating roof in itssunken position; I

FIG. 2 is an enlarged fragmentary cross-sectional view of an embodimentof the storage tank of FIG. 1, illustrating the siphon drain of theinstant invention and FIG. 3 is an enlarged plan view, partially brokenaway, of the check valve of the instant invention.

DISCLOSURE OF THE INVENTION Referring now to the drawings, and moreparticularly to FIG. 1, there is illustrated a closed storage tank ofthe floating roof type identified generally by reference numeral 10. Thestorage tank 10 serves to store liquid, for example, petroleum products,which is fed to and withdrawn from the tank 10 through shell nozzle 14which communicates with the lower portion of the tank 10.

The tank includes a circular floor 12 which is located on the ground anda generally cylindrical shell 16 extending upwardly from the peripheryof the floor 12. The shell 16 supports the edge of a fixed roof 18 thathas an upwardly extending conical shape. In addition to the shell 16,vertical support columns 20 extending upwardly from the floor 12 may beemployed to internally support the fixed roof 18.

For purpose of preventing the volatilization of the liquid stored in thetank 10 and, further, for the purpose of maintaining any vapor adjacentto the liquid, a floating roof 28 floats on and extends oversubstantially the entire surface of the liquid. As is known to thoseskilled in the art, the floating roof 28 moves vertically within thestorage tank 10 as the level of the liquid within the tank 10 changes.To prevent vapor loss, a conventional resilient sealing arrangement 30is supported from the periphery of floating roof 28 so as tofrictionally engage the shell 16, irrespective of the position of thefloating roof 28 within the tank 10. The floating roof 28 is suitablyapertured, as indicated by reference numeral 32, to accommodate supportand guidance columns 20 and is suitably apertured, as indicated byreference numeral 34, to accommodate the ladder 22. Conventional sealingarrangements (not shown) are provided on the floating roof 28 torespectively coact with the columns 20 and ladder 22 for purpose ofpreventing vapor loss.

The specific construction of the floating roof 28 in general isimmaterial to the instant invention. The floating roof 28 is a simplepan, having a rim 29 about inches high, that floats on the surface ofthe liquid product. Supporting the floating roof 28 above the floor 12during the start-up, cleaning operations, and repair operations aresupport means 41. Support means 41 are affixed to roof 28 throughsleeves 33 and are economically designed not to support any load exceptthe weight of the roof and a few inches of liquid standing above thepan.

For reasons previously discussed liquid will occasionally accumulate onthe roof causing same to sink to the bottom of the tank. It then becomesnecessary to remove all the liquid from'the tank for repair purposes.After sinking, the floating roof, including the liquidcontainedthereabove, is supported on the floor of the tank by supportmeans 41. Support means 41 will support the sunken roof as long as itisbalanced by a counter pressure of liquid in the bottom of the tankunderneath the pan. But when liquid is withdrawn from the tank to allowworkers to repair the tank and sunken pan, then the liquid underneaththe roof must be removed, thus resulting in an unbalanced force of about15 inches of liquid above the pan which cannot normally escape. Thiscauses the legs 41 to fail.

The present invention provides a method of removing the liquid from thetank without increasing the refloating roof until the roof issubstantially cleared of 65 from above to below the floating roof. If a6 inch standard pipe siphon is employed the withdrawal rate is decreasedto approximately 220 barrels/hr. Should a different size siphon be usedthen the withdrawal rate has to be changed to make certain that thewithdrawal rate is equal to or less than the rate in which liquid issiphoned from above to below the floating roof. By so regulating thewithdrawal rate and siphon rate, structural damage to the floating roof,caused by an unbalanced downward force of accumulated liquid in the pan,is eliminated. The withdrawal rate may be increased to the standardwithdrawal rate after the accumulated liquid is removed from above theroof.

Referring now to FIGS. 1 and 2, the preferred embodiment of the presentinvention includes apparatus having a siphon drain 50 fabricated from 6inch standard pipe and mitered at two joints to form an invertedU-shaped pipe. Siphon drain 50 has first and second upstanding legportions 51 and 52 respectively connected together at their respectiveupper ends by a connecting portion 53. The bottom end of leg portion 52extends through and below floating roof 28. Leg portion 51 is positionedabove floating roof 28. Leg portion 41 is positioned above floating roof28 with the bottom end being about 2 inches above the deck of thefloating roof to enable the siphon drain to flow at full capacity. Itshould be noted that leg portion 51 is positioned above nozzle 14thereby allowing liquid exiting from leg portion 52 to be withdrawnthrough nozzle 14. Support means 41 insure that leg portion 51 will notfall below nozzle 14.

A one-half inch check valve is attached to connecting portion 53 in asuitable manner, as by welding, so as to permit fluid communication withsiphon drain 50. As seen in FIG. 3 check valve 60 includes a cylindricalbody 62 having open top and bottom ends 63 and 64 respectively.Extending inwardly about the inner periphery of body 62 is horizontalmember 65 having an aperture 66 therethrough. Positioned below member 65is diametricallyextending cross bar 67 having an aperture 68therethrough. Guide pin 69 passes through apertures 66 and 68 and hasnut means'70 and 71 at its respective ends. Nut means 71, being largerin diameter than aperture 68, prevents the lower end of guide pin 69from passing completely through aperture 68. Washers 72 and 73 preventthe upper end of guide pin 69 from passing through aperture 66. Washer72 is rubber thereby effecting a seal closing off aperture 66 when valve60 is in the closed position as illustrated in FIG. 3. As the floatingroof 28 sinks, air and liquid are forced upwardly through aperture 66lifting guide pin 69 and washer 72 and allowing communication betweensiphon drain 50 and atmosphere. Check valve 60 prevents air pockets fromdeveloping in the siphon drain which would prevent the siphon fromoperating.

In operation, as the floating roof 28 accidentally sinks an air pocketis developed in the top of the siphon drain 50 below check valve 60. Theair is trapped since liquid begins to enter into both ends of legportions 51 and 52 of the siphon drain; however, check valve 60 quicklyallows for this trapped air to escape, therefore making the siphon drainoperable immediately afier it has sunk below the surface of the liquid.Eventually, floating roof 28 will land on its support means 41 on thetank floor 12. Liquid is then withdrawn from the tank at the standardwithdrawal rate through shell nozzle 14, until the liquid level reachesdown to about 1 inch below the top of the floating roof rim 29. Liquidpasses from above the roof to below the roof through seals 30, apertures32 and sleeves 33. At this time the with drawal rate is decreased toapproximately 220 barrels/hr. until the roof is cleared of liquid.Liquid from above the roof automatically flows up leg portion 51, acrossconnecting portion 53 and down leg portion 52 to below the roof at arate equal to or less than the withdrawal rate. The approximate timerequired for unloading the roof would be 8 hours for a 100 foot diametertank and 31 hours for a 200 foot diameter tank. This is a small amountof time compared to the amount of time spent in the past repairingdamage to a roof that has been overloaded.

As can be appreciated by those skilled in the art, the present inventionprovides a novel method and apparatus for removing liquid from a sunkenfloating roof of a liquid storage tank. The invention eliminates theneed for personnel entering the tank or damaging the tank shell orfloating roof. The method and apparatus for carrying out the method, aresafe and may be economically installed on new and existing floating roofstorage tanks.

While the embodiment described herein is at present considered to bepreferred, it is understood that various modifications and improvementsmay be made therein, and it is intended to cover in the appended claimsall such modifications and improvements as fall within the true spiritand scope of the invention.

What is claimed is:

l. A self-actuating siphon drain for a floating roof storage tank,adapted to drain excessive accumulations of liquid from above a sunkenfloating roof to below the floating roof, comprising: a generallyinverted U- shaped pipe having first and second upstanding leg portionsconnected together at their respective upper ends by a connectingportion, the bottom end of said second portion extending below thefloating roof and the bottom end of said first portion being positionedabove the floating roof; and check valve means attached to saidconnecting portion to allow air to escape from said pipe.

2. A siphon drain as in claim 1 wherein said check valve means onlyallows air to escape in a vertically upward direction.

1. A self-actuating siphon drain for a floating roof storage tank,adapted to drain excessive accumulations of liquid from above a sunkenfloating roof to below the floating roof, comprising: a generallyinverted U-shaped pipe having first and second upstanding leg portionsconnected together at their respective upper ends by a connectingportion, the bottom end of said second portion extending below thefloating roof and the bottom end of said first portion being positionedabove the floating roof; and check valve means attached to saidconnecting portion to allow air to escape from said pipe.
 2. A siphondrain as in claim 1 wherein said check valve means only allows air toescape in a vertically upward direction.